What is parasite species richness?

• Number of parasite species known to infect a given host

Does consider:

• the total number
• phylogenetic relationships (sometimes)
• functional traits (sometimes)

Does not consider:

• relative utilization of hosts
• effects on host fitness

What is parasite host range?

• Number of host species known to be infected by a given parasite

Does consider:

• the total number

Does not consider:

• relative utilization of hosts
• effects on host fitness
• etc.

Parasite host range

What are some potential challenges in estimating parasite host range?

Predicting parasite host range

• What are some approaches to estimating parasite host range?
• At what scale is host range defined (a country? a species?)

Predicting parasite host range

_{Dallas et al. 2017 PRSB}

Estimating host range

_{Dallas et al. 2017 PRSB}

What determines parasite host range?

• physical factors (skin thickeness)
• environmental factors?!
• host phylogenetics

Host range is just a number

The number of host species a parasite infects. How might this not be a good measure of specificity?

What is host specificity?

• Broad term related to the diversity of host species a parasite can infect
• Parasites may be specific in multiple ways
  • number of hosts (host range)
  • tissue tropism
  • morphological specificity

Different measures of specificity

• taxonomic (basically host range)
• phylogenetic
• functional

_{Dallas et al. 2020 J Animal Ecology}

What are the benefits and costs of specializing?

When would specificity be good/bad?

Maybe specificity does not exist?

_{Canard et al. 2014 American Naturalist}

…but it does.

How do we know that it does?

What other ways can we think about specificity?

• structural specificity

_{Poulin et al. 2011 Trends in Parasitology}

What other ways can we think about specificity?

• phylogenetic specificity

_{Poulin et al. 2011 Trends in Parasitology}

What other ways can we think about specificity?

• specificity across space

_{Dallas & Jordano 2022 Global Ecology and Biogeography}

Are there tradeoffs in different specificities?

_{Poulin et al. 2011 Trends in Parasitology}

End of lecture 1

Host range versus parasite species richness

• Host range is from the parasite’s perspective.

• Parasite species richness is from the host’s perspective.

What controls parasite species richness?

_{Dallas et al. 2020 J Animal Ecology}

What controls parasite species richness?

• Body size

• Geographic range size

• Host population density

• Host immune function?

_{Kamiya et al. 2013 Biological Reviews}

A note about parasite diversity

Have we sampled host species well enough to know who infects who?

The global distribution of undiscovered helminth parasites

_{Carlson et al. 2020 Proceedings B}

Predicting host-parasite interactions

• Why is it important?

• What are the features of host and parasite that allow for infection?

• What’s the goal of this?

• How do we do it?

Let’s brainstorm what information we’d want to have

Sevilleta host-parasite network

_{Dallas et al. 2017 PLOS computational biology}

Potentially important traits

_{Dallas et al. 2017 PLOS computational biology}

What traits came out of model as important?

_{Dallas et al. 2017 PLOS computational biology}

Meaning to host range/parasite species richness?

_{Dallas et al. 2017 PLOS computational biology}

Predicting potentially zoonotic parasites

_{Albery et al. 2021 Nature microbiology}

Using phylogenetic information to predict associations

_{Farrell et al. 2022 J of Animal Ecology}

Using latent network structure to predict associations

_{Poisot et al. 2023 Patterns}

Using latent network structure to predict associations

_{Poisot et al. 2023 Patterns}

What have we learned?

• What is parasite host range, specificity, and parasite species richness.
• Different ways to measure parasite specificity
• How we can predict unknown host-parasite interactions (and what this means for specificity)